احمد شکیبایی نیا

The interaction between the surface flood and the drainage system’s outflow is an important source of uncertainty in urban flood modeling. In the present study, the Weakly Compressible Smoothed Particle Hydrodynamics method was used to model the outflow from the drainage system, considering the effect of its interaction with the surface flood. To perform modeling, a new open boundary condition was defined. First, an experimental problem of dam-break propagation over a wet bed was modeled and the numerical results were compared with the experimental data. Investigations showed that the average error of the numerical model is about 2% and its maximum error is less than 4%. Then, to control the efficiency of the defined open boundary conditions, a problem of jet injection into the water tank was investigated. It was observed that the results of the numerical model are in good agreement with the experimental data. Finally, the problem of the inflow from the bottom and its interaction with the flow caused by the dam break was modeled and its results were interpreted and compared with a volume of the fluid numerical model. In general, the results showed that the developed numerical model has an acceptable accuracy in simulating complex flows.

The rapid movement of sediments, which is often induced by a very erosive and transient flow in rivers and rivers, causes a lot of geomorphology and engineering problems. Failure of the dam with a moving bed, submerged landslide, sedimentation flushing in reservoirs are just a few examples of these problems. The study of waves is challenging due to the interference of several complex physical phenomena, such as the interaction of slide-water, turbulence and complex free-surface profiles. In recent years, the increased impact of earthquake hazards on human life around the world has increased the need to find economically acceptable methods for predicting the occurrence and degradation of landslide. Considering the importance of the subject, the purpose of this research is to provide and develop an appropriate mathematical model for simulating the landslide phenomenon by Lagrangian method. Due to the ability of the Lagrange method (MPS), this method is developed to simulate the phenomenon of landslide, and the system is considered as a multidensity and multiviscosity. The results of this numerical modeling have been compared with experimental results. The results indicate the accuracy of the proposed numerical method in modeling the landslide in a rigid and deformable state.

Landslides are complex phenomena that commonly occur in mountains, oceans, bays, and reservoirs. Considering their economic and life consequences in recent years, it is necessary to find effective methods for prediction of landslides and their destructive effects. Landslide is a complicated phenomenon (especially under water), which involves a highly-reformative multiphase flow of granular materials. Considering the restrictions of the traditional mesh-based numerical models in the modeling of large deformations and the discontinuities, meshless Lagrangian (particle) methods can be the effective alternatives for simulation of landslides. The meshless Lagrangian methods such as Smoothed Particle Hydrodynamics (SPH) and Moving Particle Semi-implicit Method (MPS) provide the opportunity to model the deformations and fragmentation in sediment flow. In this research, an MPS meshless Lagrangian model has been developed for modeling of rigid and deformable landslides. In this model, the solid phase is considered as a non- Newtonian visco-plastic fluid, whose behavior is predicted using the µ (I) rheological model. The model has been validated and evaluated in comparison with the available experimental and numerical data. The water surface and the sediment profile obtained from numerical model shows a good compatibility with the experiments. The RMSE value in predicting the numerical water surface and sediment profiles of current study found to be lower compared to the other numerical methods.

Rapid sediment motion, which is usually induced by highly erosive and transient flow (e.g. in rivers), is commonly encountered in hydro-environmental problems. Dam-break flow on erodible bed, landslide, failure of river banks and reservoir sediment flushing are few examples of these problems. Accurate prediction of the complexities involved in this water-sediment two-phase system (a multiphase granular flow) is challenging for many conventional mesh-based models. Due to their ability to handle the fragmentation and deformations of interfaces, the mesh-free particle/Lagrangian methods provide a unique opportunity to handle such complexities. The objective of this paper is to develop and implement a multiphase mesh-free model, based on Moving Particle Semi-Implicit (MPS) method, for simulation of rapid sediments transport. The model considers the sediment material as a non-Newtonian viscoplastic fluid whose behaviors is predicted using an exponentially-regularized Herschel-Bulkley (H-B) rheological model. MPS method has some fluctuations non-physical pressure associated. Such fluctuations (though small) can induce some non-physical vibrations and yield criteria for granular flows will be affected. In some recent SPH and MPS studies the use of hydrostatic pressure have been proposed for cases where vertical accelerations are negligible. In cases with significant vertical acceleration, the hydrostatic pressure is not applicable. In this study, by using a smoothed thermodynamic pressure instead of hydrostatic pressure, an improved granular flow simulation is achieved. Two test cases including: dry sediment collapse and mobile-bed dam-break are modeled and compared with experimental results. Results show that sedimentation processes are well-reproduced by the developed model and numerical results show good agreement with laboratory measurements.

Mesh-free particle (Lagrangian) methods، such as moving-particle semi-implicit (MPS) and smoothed particle hydrodynamics (SPH)، are the newest methods in computational fluid dynamics، which have been applied in flow problems with large deformations and inconsistency. The aim of ths research was to develop and improve the simulation of free surface flows، using the new method of weakly compressible MPS (WC-MPS). In the MPS method، pressure is determined by solving Poisson equation. This equation is solved implicitly، which needs too much computer time. In the present research، the WC-MPS method is used to calculate pressure. In this method، as in SPH method، the state equation is used. This equation is solved explicitly، which does not occupy too much computer time. To evaluate the proposed method، the famous applied flow problem of dam break is analyzed. The program is written in C language and validations are performed for this code. To compare the Lagrangian approach with Eulerian approach، dam break is modeled by using FLOW-3D software too. The results of modeling approaches and physical models showed that both approaches have acceptable accuracy in modeling the free surface flow، but the accuracy of Lagrangian approach، especially the WC-MPS، is more than Eulerian approach. The proposed methos had some pressure oscillations، which were analyzed thereafter. Simulation of free surface flows using Weakly compressible moving-particle semi-implicit methodMesh-free particle (Lagrangian) methods، such as moving-particle semi-implicit (MPS) and smoothed particle hydrodynamics (SPH)، are the newest methods in computational fluid dynamics، which have been applied in flow problems with large deformations and inconsistency. The aim of ths research was to develop and improve the simulation of free surface flows، using the new method of weakly compressible MPS (WC-MPS). In the MPS method، pressure is determined by solving Poisson equation. This equation is solved implicitly، which needs too much computer time. In the present research، the WC-MPS method is used to calculate pressure. In this method، as in SPH method، the state equation is used. This equation is solved explicitly، which does not occupy too much computer time. To evaluate the proposed method، the famous applied flow problem of dam break is analyzed. The program is written in C language and validations are performed for this code. To compare the Lagrangian approach with Eulerian approach، dam break is modeled by using FLOW-3D software too. The results of modeling approaches and physical models showed that both approaches have acceptable accuracy in modeling the free surface flow، but the accuracy of Lagrangian approach، especially the WC-MPS، is more than Eulerian approach. The proposed methos had some pressure oscillations، which were analyzed thereafter. Simulation of free surface flows using Weakly compressible moving-particle semi-implicit method

Mesh-free particle (Lagrangian) methods, such as moving-particle semi-implicit (MPS) and smoothed particle hydrodynamics (SPH), are the newest methods in computational fluid dynamics, which have been applied in flow problems with large deformations and inconsistency. The aim of this research was to develop and improve the simulation of open-boundary free-surface flows, using the new method of weakly compressible MPS (WC-MPS). Most studies in the field of Lagrangian models are concerned with closed boundary conditions. This study, introduces a comprehensive method for MPS modeling of cases with inflow and outflow boundaries. Inflow and outflow boundaries are considered and the boundary conditions and recycling of particles are prescribed. The algorithm not only improves the inlet and outlet boundary conditions, but also reduces the pressure fluctuations at boundaries. To evaluate the proposed method, the famous applied flow problem of ogee spillway and steady shallow flow over curved bed is analyzed. The program is written in C language and validations are performed for this code. Comparison of the results of proposed model and physical models showed acceptable accuracy in modeling the free surface flows with open boundary conditions.